The present invention relates to a plastic guide such as a movable guide (a guide mounted rotatably on a single shaft, for example as a tensioner lever or a slipper) or a fixed guide (a guide used for example as a chain guide, a guide rail, or a belt guide) used in a transmission device which transmits power from a driving side to a driven side with use of a driving sprocket, a driven sprocket, and a chain entrained on those sprockets and adapted to travel circulatively or in a transmission device which transmits power from a driving side to a driven side with use of a driving pulley, a driven pulley, and a belt entrained on those pulleys and adapted to travel circulatively.
Generally, an engine or a drive unit is provided with a transmission device for the transmission of power using a chain or a belt. In the transmission device comprising a chain or a belt there is used a guide such as a movable guide or a fixed guide having a slipping function. The guide is mounted to a frame of an engine or a drive unit with mounting bolts or pins.
The movable guide for a transmission device comes into sliding contact with a circulating chain or belt to impart an appropriate tension thereto or prevent vibration and rolling of a travelling chain or belt. The fixed guide is used for preventing overstretching or overloosening of a chain or a belt when installed to a transmission device, or for preventing vibration and rolling of a travelling chain or belt, or for a mere guiding purpose.
In FIG. 7 there is illustrated a conventional plastic movable guide (tensioner lever) 100 which is used in a chain drive system. The movable guide 100 is formed integrally by molding a unitary synthetic resin material. The movable guide 100 is made up of a shoe 101 which comes into sliding contact with a travelling chain C, a vertical plate 102 disposed longitudinally on the back side of the shoe 101, a flange 103 provided along the lower edge of the vertical plate 102, and a boss 105 having a mounting hole 104 for mounting the movable guide to a housing of, for example, an engine or a drive unit. In the same figure, the numeral 102xe2x80x2 denotes a reinforcing rib.
Since the conventional plastic movable guide 100 is formed integrally by molding a unitary synthetic resin material, it is difficult to attain and maintain all of a high level of sliding contact, wear resistance and strength characteristics required as a shoe. For example, if the movable guide 100 is formed as an unreinforced plastic movable guide superior in sliding contact and wear resistance, its mechanical strength will be poor, and if its cross-sectional size is made large to compensate for the deficiency in strength, the movable guide becomes thicker and larger in size, thus giving rise to the problem that the space occupied by the movable guide when installed to a housing of, for example, an engine or a drive unit increases.
As means for solving the above-mentioned problem there has been proposed a two-layer molded plastic guide obtained by making an unreinforced resin superior in wear resistance integral with a fiber-reinforced resin as a base by injection molding (Japanese Patent Publication No. 2818795), and also proposed is a plastic guide obtained by insert molding with use of an insert member as a core which insert member is obtained by the extrusion of a steel plate (Japanese Patent Laid Open No. 254253/1996). However, when producing these plastic guides by molding, the structures of the molds used are complicated and an increase of manufacturing cost results. Further, if two kinds of resin materials are rendered integral with each other or if a metallic insert member is embedded as a core, it is impossible to absorb a change in shape caused by a difference thermal expansion coefficient, thus giving rise to the problem that the guide itself is deformed or damaged.
As another means for solution there has been proposed such a plastic movable guide 110 as shown in FIG. 8, in which a slit 117 having an opening in one side face thereof is formed in a shoe 111 of a plastic guide body which is formed integrally by molding a synthetic resin, and a reinforcing plate 118 such as a steel or iron plate is fitted in the slit 117. However, since the reinforcing plate 118 is provided in parallel with a sliding contact surface of the shoe 111 which is curved, the movable guide 110 is small in section modulus and is inferior in point of rigidity and strength. Besides, the mounting hole 114 formed in the boss 115 and the reinforcing plate 118 are spaced apart from each other and cannot be coupled together, so that the vicinity of the boss is inferior in strength. Further, since the reinforcing plate 118 is merely fitted in the opening of the slit, there also has been a problem such that the reinforcing plate is disengaged from the shoe 111 due to twisting or vibration of the shoe 111. Additionally, in the case where the reinforcing plate 118 is a metallic plate such as a steel plate, it is necessary for a metallic plate after blanking to go through a step of curving to conform to the curved surface of the shoe 111.
The present invention has been accomplished for solving the above-mentioned problems and it is an object of the invention to provide a plastic guide for a transmission device. In this plastic guide, the body of a movable or fixed guide is formed of resin in a simple shape and a reinforcing plate for reinforcing the guide body is also formed in a simple shape to permit easy assembly and prevent disengagement, and the reinforcing plate is disposed so that the section modulus of the plastic guide becomes large, thereby enhancing the flexural rigidity and strength of the guide to prevent an increase in sectional size and overall structure, with consequent reduction of weight, whereby it is intended to prevent an increase of the space occupied by the guide when mounted to the frame of an engine or a drive unit.
For achieving the above-mentioned object, in one aspect of the present invention there is provided a plastic guide for a transmission device, comprising a guide body made of a synthetic resin and a metallic reinforcing plate, the guide body comprising a shoe with whose surface a travelling chain, belt, or the like comes into sliding contact and a vertical plate disposed longitudinally on a back side of the shoe, the vertical plate having a slit formed longitudinally thereof and opening in an end portion thereof, the metallic reinforcing plate being fitted in the slit, wherein at least one window is formed in the vertical plate, a tongue piece is formed in the window, the tongue piece extending in a direction in which the reinforcing plate is fitted in the slit, the tongue piece having an expanded face for advance into the slit and also having a truncated face at an end portion thereof, and at least one concave portion is formed in the reinforcing plate and is engaged with the truncated face of the tongue piece.
In the present invention, the resin which constitutes the plastic guide body is not specially limited, but what is called an engineering plastic material superior in both wear resistance and lubricity is preferred so that the surface of sliding contact with a chain or a belt can fulfill the function required of the shoe. As the case may be, a fiber-reinforced resin may be used. The material of the reinforcing plate is not specially limited, either. As preferred examples are mentioned ferrous metals, nonferrous metals such as aluminum, magnesium, and titanium, engineering plastics superior in flexural rigidity and strength, and fiber-reinforced plastics.
Since the guide of the present invention is a plastic guide wherein the guide body provided with both shoe and vertical plate is formed integrally by molding a synthetic resin, the guide itself possesses a slipping function. Besides, a slit which opens in an end portion of the vertical plate is formed longitudinally of the vertical plate and the reinforcing plate is fitted in the slit. It follows that the reinforcing plate is provided longitudinally of the shoe, thus affording high flexural rigidity and strength. Moreover, since the reinforcing plate is fitted in the slit, the reinforcing plate can be mounted easily to the guide body, so that the manufacture of the plastic guide becomes easy and it becomes possible to automate the assembling work.
In the present invention, moreover, a tongue piece extending in the fitted direction of the reinforcing plate is formed in the window, the tongue piece having an expanded face for advancing into the slit and also having a truncated face at an end portion thereof. On the other hand, at least one recess is formed in the reinforcing plate. As the reinforcing plate is fitted into the slit, it comes into contact with the expanded face of the tongue piece. With the expanded face advanced into the slit, when the reinforcing plate is fitted into the slit, the tongue piece is deformed so as to be excluded from the slit. The tongue piece is elongated so as to facilitate the deformation.
As the reinforcing plate further advances into the slit, the recess formed therein arrives at the end portion of the tongue piece. When the recess of the reinforcing plate goes over the end portion of the tongue piece, the tongue pieces reverts to its original posture elastically and its truncated face engages the window of the reinforcing plate. In this state, the reinforcing plate is prevented from moving in a direction of dislodgment from the slit and is held positively in the guide body.